Best way to refinish scratched Billet

Could be a tough one.
You will need to sand the scratch out. it looks pretty deep so will require a fair amount of material removal.
To get it back to a similar finish I'd say use a coarse scotchbrite pad on a drill. But will likely be a matter of trial and error to see what looks best.

It’s probably hard anodized so to achieve a uniform finish, you’d have to strip it and have it redone. It’s hidden so I wouldn’t bother.

With that deep of a scratch youll have to add a small bead of weld, sand it flat, strip and recoat the entire part and hope you dont lose the pro circuit text.

Personally id just deal with it. I doubt a repair will look halfway close to the original product.